The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
There are various different types of data storage technologies used as mass storage for data processing devices and systems. The various types of storage technologies have different speeds and different costs per unit of data storage. The speed, and the cost per unit of data storage, tend to be directly related—i.e., the faster types of storage technologies also have higher costs per unit of data storage.
The various types of data storage technologies include tape, hard disk drives, and solid-state drives (i.e., collections of nonvolatile random access memory, such as Flash memory, that may be organized in a manner similar to a hard disk drive). Of these three types of storage, tape tends to be the slowest and least costly, while solid-state drives tend to be the fastest and most costly.
Because of its relatively low speed, and lack of random access, tape tends to be used only for archival purposes, if at all. However, both hard disk drives (HDDs) and solid-state drives (SSDs) remain in common use. Because of their relatively higher speed, SSDs are preferred for short access times, but HDDs are preferred for storing large amounts of data at relatively lower cost. Attempts have been made to provide hybrid drives, in which an HDD and an SSD are presented as a single device—e.g., the SSD may be used as a form of cache for the combined drive, storing most-recently-used data, particularly if those data are likely to be used again. However, either management of the two separate media had to be performed at the host system level, possibly by the central processing unit (CPU) of the host system, or the hybrid device was presented to the host system as an HDD, and therefore with the speed of an HDD, and the more limited feature set of an HDD. In addition, special vendor-specific drivers or protocols are sometimes required for such devices.